1. Field of the Invention
The present invention relates to a dry etching method for an oxide containing In, Ga, and Zn (hereinafter, referred to as “In—Ga—Zn—O”), and more particularly, to a dry etching method for an oxide semiconductor In—Ga—Zn—O in manufacturing microelectronic components such as a semiconductor element, a semiconductor integrated circuit, ° and an electrode.
2. Description of the Related Art
As described in Japanese Patent Application Laid-Open No. 2004-103957, in recent years, research and development regarding a semiconductor film made of In—Ga—Zn—O and growth conditions for the semiconductor film have been conducted.
K. Nomura et. al, Nature, vol. 432, 25 Nov. 2004, p. 488-492 and E. M. C. Fortunato et. al, Advanced Materials, 2005, 17, No. 5, p. 590-594 disclose that patterning of a produced film made of In—Ga—Zn—O or a film made of Ga—Zn—O has been performed by a lift-off method.
Regarding the dry etching, it is known that Japanese Patent Application Laid-Open No. H11-335874 discloses a technique in which a process gas containing methane is used for a dry etching method for a transparent oxide conductive film made of, for example, zinc oxide (ZnO).
Further, Japanese Patent Application Laid-Open No. H03-077209 discloses that, when a transparent conductive film made of an ITO formed on a glass substrate is subjected to dry etching, reactive dry etching using a mixture gas of hydrogen and hydrocarbon is employed while heating an ITO film. In addition, Japanese Patent Application Laid-Open No. H10-087301 discloses that a conductive film mainly made of SnO2, In2O3, and ZnO is subjected to dry etching by using hydrogen iodide.
In the conventional semiconductor dry etching, a fluorine-based gas is generally used as an etching medium.
However, the lift-off method has a problem in that a photoresist is melted and deformed at high temperature. Further, the lift-off method has another problem in that, in removing a photoresist, a patterned edge of a film to be vapor-deposited rides up, with the result that wirings provided through the patterned edge are liable to be broken and the production yield is low.
Further, the photoresist patterned by a photolithography process is used as an etching mask for reactive ion etching (RIE). In this case, there arises a problem in that it is difficult to remove a nonvolatile material, which is deposited on a surface of the resist after the etching, even by cleaning with supersonic waves.
Accordingly, it is necessary to process the film made of In—Ga—Zn—O, and various etching methods are under review in order to obtain a film having excellent reproducibility and a desired shape. There are two main types of etching methods, that is, wet etching in which a sample is immersed in a chemical agent, and dry etching in which an etching medium having a gas phase is used. In principle, in the wet etching method, etching advances isotropically, which raises a problem in that a phenomenon such as undercut of a lower portion of a mask, corrosion of a pattern due to adhesion failure between a mask and a coated film, or penetration of an etchant occurs. Further, there arises another problem in that etching residues float and remain on a device. Accordingly, replacement of the etchant is required at high frequency, which may lead to a large consumption of the etchant.
On the other hand, the dry etching method is advantageous in that chemically active ions generated in plasma are vertically made incident on a surface of a processed material due to directivity of the ions, whereby a processed shape has faithful processing characteristics for the mask pattern.
As a general dry etching method, a reactive ion etching (RIE) method is employed. A principle of the RIE is simply described as follows. An etching gas is introduced in a vacuum container having a parallel plate electrode, and high frequency power is applied to the electrode. Then, the etching gas is ionized by electrons which are rapidly accelerated due to a high frequency electric field, to thereby obtain a plasma state of the etching gas. Neutral active species (radicals) or ions generated in the plasma react on the substrate surface, which advances etching. A basic reaction mechanism is described as follows. As one example of the etching in which chemical reaction is dominant, active species are adsorbed to produce secondary products, and the active species are desorbed, thereby advancing etching. As another example of the etching in which a sputtering effect is dominant, accelerated positive ions collide with the substrate, and the substrate is physically etched.
However, the above-mentioned cited references do not disclose a specific dry etching for In—Ga—Zn—O, or include embodiments thereof. The dry etching of the film made of In—Ga—Zn—O using CF4 is disadvantageous for mass production in that the etching rate is as low as 20 angstrom/min. Further, etching selectivity with respect to a generally used insulating film (e.g., SiN or SiO) is low.
Further, in the dry etching method disclosed in Japanese Patent Application Laid-Open No. H03-077209, there arises a problem in that, in a case where an ITO is not heated, In and a carbon-based deposit are formed on the ITO film, and a predetermined configuration pattern is hardly obtained. Further, Japanese Patent Application Laid-Open No. H03-077209 does not disclose possibility of use of the dry etching for the film made of In—Ga—Zn—O, and the etching rate.
In the conventional dry etching for a semiconductor made of, for example, silicon, a fluorine-based gas is used as an etching medium in many cases. The dry etching of the film made of In—Ga—Zn—O using CF4 is disadvantageous for mass production in that the etching rate is as low as 20 angstrom/min. according to the experimental results. Further, the etching selectivity with respect to SiN, SiO, or the like generally used for an insulating film is low.
On the other hand, in a case of using a halogen gas, examples of a product that is reacted with an In—Ga—Zn—O film may include a halide containing In, Ga, and Zn, such as GaF3, GaCl2, GaCl3, GaBr3, InF3, InCl, InCl2, InCl3, InBr2, ZnF2, and ZnCl2. Those halides have a boiling point of 1000° C., 535° C., 201° C., 279° C., 1200° C., 608° C., 560° C., 600° C., 632° C., 1243° C., and 428° C., respectively. Those halides each have a high boiling point of the reactive product, a low volatility, and a low vapor pressure. Accordingly, if the substrate temperature during the etching is not set high, the reactive product cannot be desorbed and are redeposited, which raises a problem of polluting an etching chamber. Further, when a plastic film resin substrate is used, it is undesirable to perform etching using the halogen gas since the resin substrate normally has a low heat resistance. In particular, the plastic resin substrate has a low etching resistance with respect to the plasma of the halogen gas. For this reason, the substrate surface may be made rough and may have irregularities. In a case where the irregularities are formed on the substrate surface as described above, wirings may be broken by steps of the irregularities, which reduces the production yield.